The present invention relates generally to gas turbine engines, and, more specifically, to lubricating systems therein.
A gas turbine engine includes one or more rotors which support fan, compressor, and turbine blades for rotation in the engine during operation. The rotors are therefore mounted in bearings which must be suitably lubricated during operation. A typical lubricating system includes an oil tank holding lubricating supply oil which is pumped through an oil filter and oil cooler and suitably channeled to the various bearings for the lubrication thereof. Oil discharged from the bearings is collected in suitable sumps and is referred to as scavenge oil which has been heated by passage through the bearings and may contain debris or metallic chips over the course of time. The scavenge oil is suitably pumped back to the oil tank from which it repeats the lubricating circuit.
Since the lubricating oil is an important working fluid in a gas turbine engine, filtering and cooling thereof is monitored during operation. Monitoring of the oil may be conducted at various locations in the lubricating system which has various components spread axially and vertically across the extent of the engine. The lubricating system typically includes oil temperature and pressure sensors, as well as magnetic chip detectors.
Over the course of operation, the filter removes particles from the circulating oil, and therefore is periodically replaced. In the event the filter becomes prematurely filled with particles, a bypass valve is provided to divert the supply oil around the filter to ensure a continuous supply of oil to the bearings. An impending bypass sensor is typically provided around the filter to provide a visual indication of impending bypass valve operation. The bypass sensor may provide an electrical signal to a suitable gage, or may have a pop-up pin which may be visually observed when a preselected pressure drop exists across the filter.
The lubricating system also typically includes a relief valve to divert a portion of the supply oil directly back to the oil tank in the event of excessive supply oil pressure to the bearings. A suitable supply oil pump is disposed between the oil tank and the filter for circulating the supply oil through the bearings. And, separate scavenge oil pumps are typically also provided for returning the scavenge oil from the oil sumps back to the oil tank.
Most malfunctions which occur in the lubricating system are found in the various valves and sensors. Accordingly, during a service operation to uncover the source of a monitored malfunction, the various portions of the lubricating system must be accessed for visual observation of the components thereof, as well as for removal and replacement of the components if required. In a commercial, passenger carrying aircraft powered by gas turbine engines, prompt servicing of the lubrication system is of significant importance for minimizing the down time of the aircraft from revenue service.
In aircraft tail-mounted engines, the engines are positioned relatively high in the aircraft and must be accessed by providing suitable ladders or staircases. In a typical lubricating system, some portions thereof are accessible only from the top of the engine, whereas other portions thereof are accessible only from the bottom of the engine. This increases the difficulty and time in servicing the lubricating system. And, since the various components of the system are spread about in the engine, each component must be separately accessed, examined, and replaced if required which also increases the duration of the servicing operation.
Yet further, the various components of the lubricating system are crowded together with other components of the engine and makes access thereto and replacement thereof even more difficult and time consuming in view of the limited access thereto.